spring-boot如何得到一个tomcat实例(基于spring-boot_v2.0.6.RELEASE)

你的名字 2022-03-25 03:42 262阅读 0赞

在上一篇博文[spring-boot如何得到一个tomcat实例(基于spring-boot\_v1.5.14.RELEASE)][spring-boot_tomcat_spring-boot_v1.5.14.RELEASE]中我们介绍了基于spring-boot 1.5.14版本中tomcat的实例化过程,由于2.0版本之后这个实例化过程发生了很大的改变,所以本文将以2.0.6版本为基础介绍tomcat的实例化过程。([https://docs.spring.io/spring-boot/docs/2.0.6.RELEASE/reference/htmlsingle/][https_docs.spring.io_spring-boot_docs_2.0.6.RELEASE_reference_htmlsingle])

spring-boot加载tomcat的过程如下:

(1) springboot的主函数有一个注解 @SpringBootApplication,而这个注解里有一个@EnableAutoConfiguration

@Target(ElementType.TYPE)
    @Retention(RetentionPolicy.RUNTIME)
    @Documented
    @Inherited
    @SpringBootConfiguration
    @EnableAutoConfiguration     //开启自动配置
    @ComponentScan(excludeFilters = {
    	@Filter(type = FilterType.CUSTOM, classes = TypeExcludeFilter.class),
    	@Filter(type = FilterType.CUSTOM, classes = AutoConfigurationExcludeFilter.class) })
    public @interface SpringBootApplication {

(2) 相比于1.x版本,2.x版本废弃了自动配置类EmbeddedServletContainerAutoConfiguration,而使用了ServletWebServerFactoryAutoConfiguration和EmbeddedWebServerFactoryCustomizerAutoConfiguration两个自动配置类,下面我们分别来介绍一下这两个autoConfiguration

(3) 我们先看一下比较简单的TomcatWebServerFactoryCustomizer吧

@Configuration
    @ConditionalOnWebApplication
    @EnableConfigurationProperties(ServerProperties.class)
    public class EmbeddedWebServerFactoryCustomizerAutoConfiguration {
    
       
    	@Configuration
         //默认使用tomcat,因此条件满足
    	@ConditionalOnClass({ Tomcat.class, UpgradeProtocol.class }) 
    	public static class TomcatWebServerFactoryCustomizerConfiguration {
            
            // 实例化一个TomcatWebServerFactoryCustomizer实例bean,
            //这个bean实现了WebServerFactoryCustomizer接口,
            //它的customize方法负责对ConfigurableTomcatWebServerFactory进行配置
    		@Bean
    		public TomcatWebServerFactoryCustomizer tomcatWebServerFactoryCustomizer(
    				Environment environment, ServerProperties serverProperties) {
    			return new TomcatWebServerFactoryCustomizer(environment, serverProperties);
    		}
    
    	}
    
        // 由于 Server.class, Loader.class, WebAppContext.class 
        //默认情况下不存在,因此JettyWebServerFactoryCustomizerConfiguration不会生效
    	@Configuration
    	@ConditionalOnClass({ Server.class, Loader.class, WebAppContext.class })
    	public static class JettyWebServerFactoryCustomizerConfiguration {
    
    		@Bean
    		public JettyWebServerFactoryCustomizer jettyWebServerFactoryCustomizer(
    				Environment environment, ServerProperties serverProperties) {
    			return new JettyWebServerFactoryCustomizer(environment, serverProperties);
    		}
    
    	}
    
        // 由于Undertow.class, SslClientAuthMode.class默认情况下不存在,
        // 因此UndertowWebServerFactoryCustomizerConfiguration不会生效
    	@Configuration
    	@ConditionalOnClass({ Undertow.class, SslClientAuthMode.class })
    	public static class UndertowWebServerFactoryCustomizerConfiguration {
    
    		@Bean
    		public UndertowWebServerFactoryCustomizer undertowWebServerFactoryCustomizer(
    				Environment environment, ServerProperties serverProperties) {
    			return new UndertowWebServerFactoryCustomizer(environment, serverProperties);
    		}
    	}
    }

（4）然后看一下 ServletWebServerFactoryAutoConfiguration

@Configuration
    @AutoConfigureOrder(Ordered.HIGHEST_PRECEDENCE)
    @ConditionalOnClass(ServletRequest.class)
    @ConditionalOnWebApplication(type = Type.SERVLET)
    @EnableConfigurationProperties(ServerProperties.class)
    @Import({ ServletWebServerFactoryAutoConfiguration.BeanPostProcessorsRegistrar.class,
    		ServletWebServerFactoryConfiguration.EmbeddedTomcat.class,
    		ServletWebServerFactoryConfiguration.EmbeddedJetty.class,
    		ServletWebServerFactoryConfiguration.EmbeddedUndertow.class })
    public class ServletWebServerFactoryAutoConfiguration {
        
        // 实例化一个 ServletWebServerFactoryCustomizer,它的泛型参数是ConfigurableServletWebServerFactory
    	@Bean
    	public ServletWebServerFactoryCustomizer servletWebServerFactoryCustomizer(
    			ServerProperties serverProperties) {
    		return new ServletWebServerFactoryCustomizer(serverProperties);
    	}
    
       // 实例化一个TomcatServletWebServerFactoryCustomizer,它的泛型参数是TomcatServletWebServerFactory
    	@Bean
    	@ConditionalOnClass(name = "org.apache.catalina.startup.Tomcat")
    	public TomcatServletWebServerFactoryCustomizer tomcatServletWebServerFactoryCustomizer(
    			ServerProperties serverProperties) {
    		return new TomcatServletWebServerFactoryCustomizer(serverProperties);
    	}
    
    
        // 通过上面的@import引入
    	public static class BeanPostProcessorsRegistrar
    			implements ImportBeanDefinitionRegistrar, BeanFactoryAware {
    
    		private ConfigurableListableBeanFactory beanFactory;
    
    		@Override
    		public void setBeanFactory(BeanFactory beanFactory) throws BeansException {
    			if (beanFactory instanceof ConfigurableListableBeanFactory) {
    				this.beanFactory = (ConfigurableListableBeanFactory) beanFactory;
    			}
    		}
    
    		@Override
    		public void registerBeanDefinitions(AnnotationMetadata importingClassMetadata,
    				BeanDefinitionRegistry registry) {
    			if (this.beanFactory == null) {
    				return;
    			}
                //这边的处理跟v1.x版本是一致的, 
                //从beanFactory中获取一个WebServerFactoryCustomizerBeanPostProcessor实例bean,
                //如果不存在,则主动new一个
    			registerSyntheticBeanIfMissing(registry,
    					"webServerFactoryCustomizerBeanPostProcessor",
    					WebServerFactoryCustomizerBeanPostProcessor.class);
    			registerSyntheticBeanIfMissing(registry,
    					"errorPageRegistrarBeanPostProcessor",
    					ErrorPageRegistrarBeanPostProcessor.class);
    		}
    
    		private void registerSyntheticBeanIfMissing(BeanDefinitionRegistry registry,
    				String name, Class<?> beanClass) {
    			if (ObjectUtils.isEmpty(
    					this.beanFactory.getBeanNamesForType(beanClass, true, false))) {
    				RootBeanDefinition beanDefinition = new RootBeanDefinition(beanClass);
    				beanDefinition.setSynthetic(true);
    				registry.registerBeanDefinition(name, beanDefinition);
    			}
    		}
    
    	}
    
    }

ServletWebServerFactoryAutoConfiguration 主要做了四件事:

*   **注1**：通过@import引入ServletWebServerFactoryConfiguration的几个子类:EmbeddedTomcat、EmbeddedJetty和EmbeddedUndertow,而事实上最终只有EmbeddedTomcat起作用了,如下图,EmbeddedJetty和EmbeddedUndertow缺少依赖的java类,因此不会生效,而唯一生效的EmbeddedTomcat只做了一件事：实例化了一个TomcatServletWebServerFactory的bean，这个bean在 **注4** 会用到

![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3NvbmdfamF2YQ_size_16_color_FFFFFF_t_70][]

*  **注2**：实例化一个 ServletWebServerFactoryCustomizer的bean(它实现了WebServerFactoryCustomizer接口),它对ConfigurableServletWebServerFactory(它继承了WebServerFactory接口)进行配置

// ServletWebServerFactoryCustomizer实现了WebServerFactoryCustomizer接口
    // ConfigurableServletWebServerFactory继承了WebServerFactory接口
    // 之所以强调这些,因为在 注4 总会用到哦
    public class ServletWebServerFactoryCustomizer implements
    		WebServerFactoryCustomizer<ConfigurableServletWebServerFactory>, Ordered {
    
    	private final ServerProperties serverProperties;
    
    	public ServletWebServerFactoryCustomizer(ServerProperties serverProperties) {
    		this.serverProperties = serverProperties;
    	}
    
    	@Override
    	public int getOrder() {
    		return 0;
    	}
    
    	@Override
    	public void customize(ConfigurableServletWebServerFactory factory) {
    		PropertyMapper map = PropertyMapper.get().alwaysApplyingWhenNonNull();
    		map.from(this.serverProperties::getPort).to(factory::setPort);
    		map.from(this.serverProperties::getAddress).to(factory::setAddress);
    		map.from(this.serverProperties.getServlet()::getContextPath)
    				.to(factory::setContextPath);
    		map.from(this.serverProperties.getServlet()::getApplicationDisplayName)
    				.to(factory::setDisplayName);
    		map.from(this.serverProperties.getServlet()::getSession).to(factory::setSession);
    		map.from(this.serverProperties::getSsl).to(factory::setSsl);
    		map.from(this.serverProperties.getServlet()::getJsp).to(factory::setJsp);
    		map.from(this.serverProperties::getCompression).to(factory::setCompression);
    		map.from(this.serverProperties::getHttp2).to(factory::setHttp2);
    		map.from(this.serverProperties::getServerHeader).to(factory::setServerHeader);
    		map.from(this.serverProperties.getServlet()::getContextParameters)
    				.to(factory::setInitParameters);
    	}

*  **注3**：实例化一个 TomcatServletWebServerFactoryCustomizer的bean,它对TomcatServletWebServerFactory（它是WebServerFactory的一个实现类）进行配置

// TomcatServletWebServerFactoryCustomizer实现了WebServerFactoryCustomizer接口
    // TomcatServletWebServerFactory实现了WebServerFactory接口
    // 在 注4 中会用到哦
    public class TomcatServletWebServerFactoryCustomizer
    		implements WebServerFactoryCustomizer<TomcatServletWebServerFactory>, Ordered {
    
    	private final ServerProperties serverProperties;
    
    	public TomcatServletWebServerFactoryCustomizer(ServerProperties serverProperties) {
    		this.serverProperties = serverProperties;
    	}
    
    	@Override
    	public int getOrder() {
    		return 0;
    	}
    
    	@Override
    	public void customize(TomcatServletWebServerFactory factory) {
    		ServerProperties.Tomcat tomcatProperties = this.serverProperties.getTomcat();
    		if (!ObjectUtils.isEmpty(tomcatProperties.getAdditionalTldSkipPatterns())) {
    			factory.getTldSkipPatterns()
    					.addAll(tomcatProperties.getAdditionalTldSkipPatterns());
    		}
    		if (tomcatProperties.getRedirectContextRoot() != null) {
    			customizeRedirectContextRoot(factory,
    					tomcatProperties.getRedirectContextRoot());
    		}
    		if (tomcatProperties.getUseRelativeRedirects() != null) {
    			customizeUseRelativeRedirects(factory,
    					tomcatProperties.getUseRelativeRedirects());
    		}
    	}

*  **注4**：通过@import引入BeanPostProcessorsRegistrar,进而通过BeanPostProcessorsRegistrar确保实例化一个WebServerFactoryCustomizerBeanPostProcessor实例bean,这个BeanPostProcessor的作用其实跟1.x版本中的EmbeddedServletContainerCustomizerBeanPostProcessor作用是一样的(摘抄部分源码如下),

@Override
    	public Object postProcessBeforeInitialization(Object bean, String beanName)
    			throws BeansException {
            // 当bean是WebServerFactory的实例时则进行postProcessBeforeInitialization处理
            // 在注1中我们实例化了一个TomcatServletWebServerFactory,在这里可以派上用场了
            //都是实现或继承了webServerFactory
    		if (bean instanceof WebServerFactory) {
    			postProcessBeforeInitialization((WebServerFactory) bean);
    		}
    		return bean;
    	}
    
    
    	@SuppressWarnings("unchecked")
    	private void postProcessBeforeInitialization(WebServerFactory webServerFactory) {
    		   // 使用WebServerFactoryCustomizer的customize方法对webServerFactory进行配置,
    
               LambdaSafe
    				.callbacks(WebServerFactoryCustomizer.class, getCustomizers(),
    						webServerFactory)
    				.withLogger(WebServerFactoryCustomizerBeanPostProcessor.class)
    				.invoke((customizer) -> customizer.customize(webServerFactory));
    	}
    
    	private Collection<WebServerFactoryCustomizer<?>> getCustomizers() {
    		if (this.customizers == null) {
    			// Look up does not include the parent context
    			this.customizers = new ArrayList<>(getWebServerFactoryCustomizerBeans());
                // 对所有的WebServerFactoryCustomizer按照Orderd进行排序
    			this.customizers.sort(AnnotationAwareOrderComparator.INSTANCE);
    			this.customizers = Collections.unmodifiableList(this.customizers);
    		}
    		return this.customizers;
    	}
    
        // 从beanFactory中找到所有的WebServerFactoryCustomizer实例bean
        // 步骤(3)中 EmbeddedWebServerFactoryCustomizerAutoConfiguration
        //实例化了一个TomcatWebServerFactoryCustomizer的bean,
        //这个bean实现了WebServerFactoryCustomizer接口,
        // 在注2和注3中ServletWebServerFactoryAutoConfiguration实例化的 
        //ServletWebServerFactoryCustomizer和TomcatServletWebServerFactoryCustomizer
        //都实现了WebServerFactoryCustomizer接口,
       //因此在这里至少有3个我们已经知道的WebServerFactoryCustomizer可以在这里找到
    	private Collection<WebServerFactoryCustomizer<?>> getWebServerFactoryCustomizerBeans() {
    		return (Collection) this.beanFactory
    				.getBeansOfType(WebServerFactoryCustomizer.class, false, false).values();
    	}

对于上面的 注1~ 注4,都出现了WebServerFactory或它的子类,我们可以用下面这张类图来阐述他们的关系:TomcatServletWebServerFactory实现了ConfigurableTomcatWebServerFactory接口,而ConfigurableTomcatWebServerFactory接口又继承了WebServerFactory接口

![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3NvbmdfamF2YQ_size_16_color_FFFFFF_t_70 1][]

(5) 跟1.x版本中的情况一样,以上步骤的主要目的就是实例化一个TomcatServletWebServerFactory,然后通过各个WebServerFactoryCustomizer对这个factory进行定制，最终得到一个完整的TomcatServletWebServerFactory，然后它的getWebServer方法就得到了一个tomcat实例,至此tomcat的实例过程讲解完毕。

![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3NvbmdfamF2YQ_size_16_color_FFFFFF_t_70 2][]

最后我们再总结一下对于spring-boot v1.x版本和v2.x版本，tomcat的实例化过程的具体区别

*   WebServerFactoryCustomizerBeanPostProcessor替代了EmbeddedServletContainerCustomizerBeanPostProcessor
 *   WebServerFactory及其子类替代了ConfigurableEmbeddedServletContainer及其子类
 *   WebServerFactoryCustomizer及其子类替代了EmbeddedServletContainerCustomizer及其子类
 *   ServerProperties在2.x中只是一个普通的配置类,而在1.x中它比较复杂，如下图是它的类关系图，它还是EmbeddedServletContainerCustomizer的实现类,并且会作为一个默认实例化的bean起作用，在2.x中ServerProperties主要是作为各个Customizer的构造参数,然后在customize方法中使用。

![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3NvbmdfamF2YQ_size_16_color_FFFFFF_t_70 3][]

[spring-boot_tomcat_spring-boot_v1.5.14.RELEASE]: https://blog.csdn.net/song_java/article/details/81190449
[https_docs.spring.io_spring-boot_docs_2.0.6.RELEASE_reference_htmlsingle]: https://docs.spring.io/spring-boot/docs/2.0.6.RELEASE/reference/htmlsingle/
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